[tex] {\text{Amount of energy releases from an earthquake is given by }}E = {10^{18.4}} ergs \hfill \\
{\text{Released energy can be measured on Richter scale using the formula}} \hfill \\
M = \frac{2}{3}{\log _{10}}\left( {\frac{E}{{{{10}^{11.8}}}}} \right) \hfill \\
{\text{On substituting the value of }}E{\text{ in the given formula, we get}} \hfill \\
M = \frac{2}{3}{\log _{10}}\left( {\frac{{{{10}^{18.4}}}}{{{{10}^{11.8}}}}} \right) \hfill \\
\Rightarrow M = \frac{2}{3}{\log _{10}}\left( {{{10}^{18.4 - 11.8}}} \right) \hfill \\
\Rightarrow M = \frac{2}{3}{\log _{10}}\left( {{{10}^{6.6}}} \right) \hfill \\
\Rightarrow M = \frac{2}{3} \times 6.6 \hfill \\
\Rightarrow M = 2 \times 2.2 \hfill \\
\Rightarrow M = 4.4 \hfill \\
\[{\text{Thus, the correct option is C}}.\]
[/tex]
